ABSTRACT
Very Low Density Lipoprotein Receptor (VLDLR) is an apolipoprotein E receptor involved in synaptic plasticity, learning, and memory. However, it is unknown how VLDLR can regulate synaptic and cognitive function. In the present study, we found that VLDLR is present at the synapse both pre- and post-synaptically. Overexpression of VLDLR significantly increases, while knockdown of VLDLR decreases, dendritic spine number in primary hippocampal cultures. Additionally, knockdown of VLDLR significantly decreases synaptophysin puncta number while differentially regulating cell surface and total levels of glutamate receptor subunits. To identify the mechanism by which VLDLR induces these synaptic effects, we investigated whether VLDLR affects dendritic spine formation through the Ras signaling pathway, which is involved in spinogenesis and neurodegeneration. Interestingly, we found that VLDLR interacts with RasGRF1, a Ras effector, and knockdown of RasGRF1 blocks the effect of VLDLR on spinogenesis. Moreover, we found that VLDLR did not rescue the deficits induced by the absence of Ras signaling proteins CaMKIIα or CaMKIIß. Taken together, our results suggest that VLDLR requires RasGRF1/CaMKII to alter dendritic spine formation.
Subject(s)
Calcium-Calmodulin-Dependent Protein Kinase Type 2/metabolism , Dendritic Spines/metabolism , Receptors, LDL/metabolism , ras-GRF1/metabolism , Animals , COS Cells , Cell Adhesion Molecules, Neuronal/pharmacology , Cell Membrane/drug effects , Cell Membrane/metabolism , Cells, Cultured , Chlorocebus aethiops , Dendritic Spines/drug effects , Extracellular Matrix Proteins/pharmacology , Gene Knockdown Techniques , Hippocampus/cytology , Mice, Knockout , Models, Biological , Nerve Tissue Proteins/metabolism , Nerve Tissue Proteins/pharmacology , Neurons/drug effects , Neurons/metabolism , Protein Binding/drug effects , Rats, Sprague-Dawley , Receptors, N-Methyl-D-Aspartate/metabolism , Reelin Protein , Serine Endopeptidases/pharmacology , Synapses/drug effects , Synapses/metabolism , Synaptophysin/metabolismABSTRACT
Alzheimer's disease (AD) risk genes alter brain structure and function decades before disease onset. Apolipoprotein E (APOE) is the strongest known genetic risk factor for AD, and a related gene, apolipoprotein J (APOJ), also affects disease risk. However, the extent to which these genes affect brain structure in young adults remains unclear. Here, we report that AD risk alleles of these two genes, APOE-ε4 and APOJ-C, cumulatively alter brain volume in young adults. Using voxel-based morphometry (VBM) in 57 individuals, we examined the entorhinal cortex, one of the earliest brain regions affected in AD pathogenesis. Apolipoprotein E-ε4 carriers exhibited higher right entorhinal cortex volume compared to non-carriers. Interestingly, APOJ-C risk genotype was associated with higher bilateral entorhinal cortex volume in non-APOE-ε4 carriers. To determine the combined disease risk of APOE and APOJ status per subject, we used cumulative odds ratios as regressors for volumetric measurements. Higher disease risk corresponded to greater right entorhinal cortex volume. These results suggest that, years before disease onset, two key AD genetic risk factors may exert influence on the structure of a brain region where AD pathogenesis takes root.
ABSTRACT
We recently reported that the tetra(ethylene glycol) derivative of benzothiazole aniline, BTA-EG4, acts as an amyloid-binding small molecule that promotes dendritic spine density and cognitive function in wild-type mice. This raised the possibility that BTA-EG4 may benefit the functional decline seen in Alzheimer's disease (AD). In the present study, we directly tested whether BTA-EG4 improves dendritic spine density and cognitive function in a well-established mouse model of AD carrying mutations in APP, PS1 and tau (APPswe;PS1M146V;tauP301L, 3xTg AD mice). We found that daily injections of BTA-EG4 for 2 weeks improved dendritic spine density and cognitive function of 3xTg AD mice in an age-dependent manner. Specifically, BTA-EG4 promoted both dendritic spine density and morphology alterations in cortical layers II/III and in the hippocampus at 6-10 months of age compared to vehicle-injected mice. However, at 13-16 months of age, only cortical spine density was improved without changes in spine morphology. The changes in dendritic spine density correlated with Ras activity, such that 6-10 month old BTA-EG4 injected 3xTg AD mice had increased Ras activity in the cortex and hippocampus, while 13-16 month old mice only trended toward an increase in Ras activity in the cortex. Finally, BTA-EG4 injected 3xTg AD mice at 6-10 months of age showed improved learning and memory; however, only minimal improvement was observed at 13-16 months of age. This behavioral improvement corresponds to a decrease in soluble Aß 40 levels. Taken together, these findings suggest that BTA-EG4 may be beneficial in ameliorating the synaptic loss seen in early AD.
Subject(s)
Alzheimer Disease/complications , Aniline Compounds/therapeutic use , Cognition Disorders/drug therapy , Cognition Disorders/etiology , Dendritic Spines/drug effects , Hippocampus/pathology , Age Factors , Alzheimer Disease/drug therapy , Alzheimer Disease/genetics , Amyloid beta-Protein Precursor/genetics , Aniline Compounds/pharmacology , Animals , Disease Models, Animal , Hippocampus/ultrastructure , Humans , Male , Maze Learning/drug effects , Mice , Mice, Transgenic , Mutation/genetics , Presenilin-1/genetics , tau Proteins/geneticsABSTRACT
The tetra(ethylene glycol) derivative of benzothiazole aniline, BTA-EG4, is a novel amyloid-binding small molecule that can penetrate the blood-brain barrier and protect cells from Aß-induced toxicity. However, the effects of Aß-targeting molecules on other cellular processes, including those that modulate synaptic plasticity, remain unknown. We report here that BTA-EG4 decreases Aß levels, alters cell surface expression of amyloid precursor protein (APP), and improves memory in wild-type mice. Interestingly, the BTA-EG4-mediated behavioral improvement is not correlated with LTP, but with increased spinogenesis. The higher dendritic spine density reflects an increase in the number of functional synapses as determined by increased miniature EPSC (mEPSC) frequency without changes in presynaptic parameters or postsynaptic mEPSC amplitude. Additionally, BTA-EG4 requires APP to regulate dendritic spine density through a Ras signaling-dependent mechanism. Thus, BTA-EG4 may provide broad therapeutic benefits for improving neuronal and cognitive function, and may have implications in neurodegenerative disease therapy.
Subject(s)
Aniline Compounds/pharmacology , Benzothiazoles/pharmacology , Dendritic Spines/drug effects , Ethylene Glycols/pharmacology , Genes, ras/drug effects , Neurogenesis/drug effects , Amyloid beta-Protein Precursor/genetics , Animals , Biotinylation , COS Cells , Cerebrovascular Circulation/drug effects , Chlorocebus aethiops , Cognition Disorders/chemically induced , Cognition Disorders/psychology , Enzyme-Linked Immunosorbent Assay , Excitatory Postsynaptic Potentials/drug effects , Immunohistochemistry , Long-Term Potentiation/physiology , Male , Maze Learning/physiology , Mice , Mice, Inbred C57BL , Mice, Knockout , Neurons/drug effects , Receptors, AMPA/drug effectsABSTRACT
Histone deacetylase inhibitors (HDACIs) alter gene expression epigenetically by interfering with the normal functions of HDAC. Given their ability to decrease Aß levels, HDACIs are a potential treatment for Alzheimer's disease (AD). However, it is unclear how HDACIs alter Aß levels. We developed two novel HDAC inhibitors with improved pharmacological properties, such as a longer half-life and greater penetration of the blood-brain barrier: mercaptoacetamide-based class II HDACI (coded as W2) and hydroxamide-based class I and IIHDACI (coded as I2) and investigated how they affect Aß levels and cognition. HDACI W2 decreased Aß40 and Aß42 in vitro. HDACI I2 also decreased Aß40, but not Aß42. We systematically examined the molecular mechanisms by which HDACIs W2 and I2 can decrease Aß levels. HDACI W2 decreased gene expression of γ-secretase components and increased the Aß degradation enzyme Mmp2. Similarly, HDACI I2 decreased expression of ß- and γ-secretase components and increased mRNA levels of Aß degradation enzymes. HDACI W2 also significantly decreased Aß levels and rescued learning and memory deficits in aged hAPP 3xTg AD mice. Furthermore, we found that the novel HDACI W2 decreased tau phosphorylation at Thr181, an effect previously unknown for HDACIs. Collectively, these data suggest that class II HDACls may serve as a novel therapeutic strategy for AD.
